This invention relates to organic polyhydroxy compounds and, more particularly to a method for improving the compatibility or miscibility of two or more polyols with each other and to a polyol mixture for use in making polyaddition products by reaction with organic polyisocyanates.
This invention especially relates to normally incompatible polyol mixtures comprising at least one high molecular weight polyol and at least one low molecular weight polyol and their conversion to polyol products with greater resistance to phase separation. The modified polyol products obtained are useful in making polyaddition products by reaction with organic polyisocyanates since the modified polyol products still possess polyhydroxyl functionality.
It is known from German Offenlegungsschriften Nos. 1,770,703 and 2,309,861 to use mixtures of polyols which are incompatible with each other for the preparation of polyurethanes. In this way, it is possible to obtain end products which have improved properties, for example, greater heat resistance and higher impact strength. While the use of a mixture of incompatible polyols has the advantages just described, this mixture of polyols also has disadvantages in storage and in methods of processing.
When polyol systems of this kind, which have been thoroughly mixed, are stored for even a relatively short time, i.e., several hours to three days, the mixture separates into two phases so that it must be very vigorously mixed again each time before use in order to insure that the individual components in the mixture will be uniformly distributed through the mixture in the correct proportions. The incompatible polyol mixtures often exhibit miscibility on heating to slightly elevated temperatures. They cloud out, however, at a specific temperature known as the "Cloud Point" when the temperature of the mixture is lowered, and the separation often is accelerated by lower temperatures.
Storage of incompatible polyol mixtures sometimes is accompanied by solidification of one or more of the separated phases. Such solid separation can cause pluggage in metering of components to polyurethane processing machines and make for difficulties in consistent operations. In addition any separated solid phase obtained in storage must be melted and mixed to insure consistent composition as well as to avoid pluggage.
When using polyol mixtures which may separate in from several hours to several days, it is impossible to insure that the individual components of a polyol mixture are uniformly distributed throughout the mixture in the correct proportion unless the polyol mixture is vigorously mixed throughout its storage.
The prior art has attempted to overcome the above-noted problems. As shown in U.S. Pat. No. 4,029,593, the presence of 0.05 to 5 percent by weight of an inert surface-active inorganic material having a specific surface of about 10 to about 800 m.sup.2 /g in a polyol mixture of two partially incompatible polyols, optionally, with auxiliary agents and additives of the kind commonly used for producing polyurethanes can, to a large extent, prevent rapid settling of one or more components of a mixture of incompatible polyols or partly compatible polyols.
Similarly, U.S. Pat. No. 3,993,576 relates to the same problem and solves that problem by adding a derivative of butylene glycol or propylene glycol to the polyol mix.
It is an object of this invention to provide mixtures of polyols stabilized against separation. It is another object of this invention to provide a method for stabilizing a mixture of polyols by converting them to a mixture less prone to separate while maintaining a useful hydroxyl functionality. It is a further object of this invention to form a polyol mixture which shows less tendency to separation into phases and which does not require additives not commonly present in polyurethanes. It is another object of this invention to produce a polyol mixture reaction product resistant to phase separation at or slightly above room temperature. It is another object of this invention to reduce the tendency for a polyol mixture to separate into phases without markedly altering its useful hydroxyl functionality for reaction with polyisocyanates.